1. Field of the Invention
The subject invention relates to a system for transmitting and receiving radio signals to street light assemblies including light emitting diode (LED) arrays.
2. Description of the Prior Art
Proven metrics indicate that at least a fifty percent (50%) energy savings is possible when high-intensity discharge (H.I.D.) street lamps are replaced with properly designed LED light assemblies. The expected life of LED light assemblies can exceed 10-12 years, compared to a nominal 2-3 year life of H.I.D. lamps. An LED retrofit of standard H.I.D. street lights is beneficial for the environment, and the energy related cost savings allow the LED light assemblies to pay for themselves in approximately five years. Energy savings can be even greater with a system for intelligent control and dimming, which further reduces energy consumption and increases the expected life of the LEDs. The unique characteristics of LEDs permits virtually instantaneous on-off cycling, which is impossible with H.I.D. lamps. The LEDs can typically be dimmed up to fifty percent (50%) without a significant change in perceived brightness. In addition, the LEDs do not require a costly dimmable ballast, which is required for each H.I.D. lamp. Therefore, municipalities or other governing organizations in geographical territories are desirous of replacing traditional H.I.D. lamps used in street lights including light emitting diode arrays. The initial cost of purchasing and installing the LED light assemblies is the only barrier preventing them from doing so.
Existing systems which control street light assemblies in geographical territories have proven useful in reducing the energy consumption of H.I.D. lamps, but are an add-on that is cumbersome and expensive to install and maintain. An existing system capable of controlling street lights utilizes an electrical power line modem system using high frequency signaling impressed on existing power conductors. An example of such a system is disclosed in U.S. Pat. No. 4,675,579, assigned to James H. Hardy et. al. The Hardy '579 patent discloses the use of electrical power lines for transmitting carrier signals to traditional street light assemblies, which consume prodigious amounts of electrical power, to control and dim the traditional lights. The carrier signals are transmitted over conductors in underground ducts or on overhead poles from a local controller box to up to a group of fifty (50) street lights sharing an electrical line. The local controller boxes are operated by remote control or programmed clockwork.
As alluded to above, integrating a power line modem system into a municipality or other geographical territory to control and dim street lights including LEDs requires a costly and cumbersome addition to existing infrastructure in the geographical territory. In a typical power line modem system existing today, a group of about one hundred (100) street lights sharing a local controller box, electrical transformer, and electrical line comprise a single communication group, which is effectively isolated from other groups, e.g., by the transformers. Signals cannot reliably cross electrical transformer isolated groups if they do not share a common electrical line. Therefore, the municipality must install a costly modem before the electrical transformer in each group to maintain signal integrity and remotely control the street lights in each group. However, interconnecting all of the modems to a central system controller remains problematic, i.e. the signaling is only useful in relatively small groups of street lights. The municipality may also have to install additional electrical transformers to segregate the street lights into appropriately sized groups. A medium sized municipality with 100,000 street lights might require approximately 1,000 electrical transformers, and 1,000 power line modems. Most municipalities can not afford this huge initial cost.
Another example of such a light control system is a radio mesh system, such as the system disclosed in U.S. Pat. No. 7,333,903 to Jeff. D. Walter. The Walter '903 patent discloses a master controller transmitting and receiving radio signals over a radio frequency to and from traditional street light assemblies. The radio signals from the master controller are received by one of the streets lights and transmitted to the other street lights by a handing-off scheme, whereby they form a network. However, the radio signals are subject to interference from numerous other devices, like portable telephones, microwaves, and video monitors, emitting signals on the same radio frequency, which could easily corrupt the communication. The range of frequencies available for use by commercially sold mesh systems is very limited, and the signals are often subject to multi-path distortion and severe attenuation from building walls, people, and other objects. In addition, the master controller in this type of system is oftentimes incapable of transmitting the radio signals over ranges long enough to control municipal street light assemblies. Therefore, mesh radio systems are not reliable enough for the safety critical control of street light assemblies. A publication by Echelon Corporation, titled Radio Frequency Control Networking: Why Poor Reliability Today Hampers What Could Be a Viable Technology in the Future, by Abhay Gupta and Michael R. Tennefoss, discloses the unreliability and other disadvantages of power line systems, mesh radio systems and other existing networked light control systems.
Because it is difficult to transmit radio signals from a central transceiver in a municipality or other geographical territory over a wide geographical territory and into and around buildings, the radio systems used by public safety personnel (police, fire, EMS, etc.) include repeaters which receive and re-transmit radio signals. The repeaters assure a strong radio signal throughout the geographical territory to reach public safety personnel in, under, and around buildings and other objects. For example, repeaters are used to assure safety critical radio signals are received by police in, under, and around the buildings of New York City. The frequencies used by municipalities for public safety personnel are assigned by the FCC and are basically clear channels free of interference from nearby frequencies. These public safety frequencies are used a relatively small percentage of the time for transmitting voice communications.
There remains a great need for a reliable and economical LED light assembly control system for municipal street lights which reduces energy consumption and can be controlled yet is an affordable initial cost for municipalities.